libctf, dump: correctly dump non-root-visible types

The flag test when dumping non-root-visible tyeps was doubly wrong: the
flags word is a *bitfield* containing CTF_ADD_ROOT as one possible
value, so needs | and & testing, not just ==, and CTF_ADD_NONROOT is 0,
so cannot be tested for this way: one must check for the non-presence of
CTF_ADD_ROOT.

libctf/
	* ctf-dump.c (ctf_dump_format_type): Fix non-root flag test.